This is an R script that will extract excel files from Outlook - kianweelee/Extract-excel-from-Outlook-into-R ...

Go to File > Open and select your Excel file. After opening the file in Excel Safe Mode, save it in a different format through File > Save As, selecting either .csv or .xls.

If your Excel files are opening in Notepad on Windows PC, here's how you can reset the settings to make .xls, .xlsx, etc files open in Excel.

The file can be successfully loaded in both MS Excel and LibreOffice Calc. However, it was not created by Excel, but by some other tool. If I open it in Excel and save it as a new file, readxl can ...

If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.